I love tanks where you can see it from both sides of the wall.
I too would not want a saltwater tank. To much work, and to me, for some reason, freshwater feels more peaceful and serene to me.
I'd probably want something for aquatic turtles (aka BIG tank) set into a wall somehow, and/or incorporate freshwater fish in that tank and/or around that that tank. (The turtle tank would be the main focal point of the piece) the freshwater tanks incorporated with the turtle tank would be Amazon and/or Asian themed dedicated to Betta/s, Albino Corycats, Cardinal Tetras, Kuhlii Loaches, Red Platys, Guppies, Bristlenose Catfish and some other random asian fish, Tetra fish, and one section dedicated to Goldfish and other cold water fish and another for Discus. (aka more BIG tankness.) The big/small tanks together concept might work out in case I want to one day trade the discus or goldfish for something else or the smaller fish for something else.
I can dream.. Siigghh.. One day I might have enough money for something like this...